About 1% of all iPhones Are on T-Mobile USA's Network. Really...

T-Mobile doesn’t carry the iPhone. Its soon-to-be-owner does, however. And, it was relatively simple to take an iPhone prior to the iPhone 4, jailbreak it, unlock it and throw in a T-Mobile SIM card use on T-mobile’s network. The result is not ideal since while voice T-Mobile and AT&T use different 3G frequencies, only slower EDGE data connections can be used when on T-Mobile. The iPhone 4 with its microSIM presents even more of a challenge since the additional step of shaving T-Mobile’s conventional sized SIM card down to a microSIM form factor.